Grantee Research Project Results
Final Report: The Microbial and Transformations of Arsenic in Anoxic Waters
EPA Grant Number: R823222Title: The Microbial and Transformations of Arsenic in Anoxic Waters
Investigators: Morel, Francois M.
Institution: Princeton University
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1995 through September 30, 1998
Project Amount: $356,082
RFA: Exploratory Research - Environmental Biology (1995) RFA Text | Recipients Lists
Research Category: Biology/Life Sciences , Human Health , Aquatic Ecosystems
Objective:
Arsenic is released from a variety of sources into the environment, and may cause severe health and ecological effects. This project focused on the transformations of arsenic in anoxic waters and sediments. More specifically, the long-term goals of this project were to elucidate the chemical and biological mechanisms that control the precipitation and dissolution of arsenic in anaerobic sediments and to quantify the consequences of these processes in determining the potential release of this toxic element to the water column.
Summary/Accomplishments (Outputs/Outcomes):
The major focus of this project was the respiration of arsenate, As(V), by bacteria in anoxic environments. As first reported in our letter to Nature (Ahmann, et al., 1994), we have discovered that some bacteria are able to grow by using arsenate as a terminal electron acceptor in respiration, producing arsenate, As(III), in the process. Based on this discovery, we proceeded to document the microbial reduction of the relatively immobile arsenate to the more mobile arsenite in anaerobic sediments, and to study the conditions for arsenate reduction and precipitation of arsenite as the arsenic trisulfide solid.
We first isolated two bacterial strains, Geospirilum arsenophilus and Desulfotomaculum auripigmentum, which grow by dissimilatory reduction of arsenate, As(V), and characterized both organisms in terms of their metabolic capabilities. We also have studied the conditions for microbial precipitation of arsenic trisulfide in cultures of D. auripigmentum and elucidated the reasons why it does not occur in other cultures.
G. arsenophilus and D. auripigmentum have very different metabolic capabilities. One can reduce N(V) (nitrate) as well as As(V), while the other can grow on S(VI) (sulfate) as well as As(V). In addition, G. arsenophilus is gram-negative, D. auripigmentum is gram-positive and, according to 16S ribosomal RNA sequencing, the two organisms are phylogenetically quite distant. In addition to reducing As(V), D. auripigmentum precipitates arsenite, As (III), as As2S3 in S-containing medium. This precipitation occurs, at least in part, intracellularly and under conditions where no chemical precipitation is observed.
To allow us to generalize our findings, we have pursued a more fundamental biochemical understanding of As(V) respiration using Sulfurospirillum barnesii, strain SES-3. We have found that the enzyme used for arsenate respiration is significantly different from those used for arsenate detoxification by other bacteria. The respiratory arsenate reductase is membrane bound, unlike the previously described arsenate reductases of E. coli and S. aureaus (i.e., ArsC enzymes). The respiratory arsenate reductase comprises three highly hydrophobic polypeptides with molecular masses of approximately 65, 30, and 22 kDa. N-terminal sequencing of these proteins reveals the 65 kDa protein to be very similar to the HydB protein of Wolinella succinogenes, the main subunit of a Ni/Fe-hydrogenase. No matches were found in the database to the N-terminal sequences of the 30 and 22 kDa proteins. The gene encoding the 30 kDa protein has been sequenced, and we are working on sequencing the entire operon containing these genes.
These results have modified radically our understanding of the processes that control the fate of arsenic in aquatic systems. First, it appears that arsenate respiration is likely widespread among bacterial phyla and common in contaminated anoxic environs. Further, the microbial precipitation of arsenic trisulfide, puts into question the general assumption that reduction of As(V) to As(III) makes As more mobile in the environment. On the contrary, As2S3 precipitation may provide a permanent sink for As in anaerobic sediments. Our new biochemical understanding of As(V) respiration and our genetic information will allow us and others to study this process in the field.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 4 publications | 4 publications in selected types | All 4 journal articles |
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Ahmann D, Krumholz LR, Hemond HF, Lovley DR, Morel FMM. Microbial mobilization of arsenic from sediments of the Aberjona Watershed. Environmental Science & Technology 1997;31(10):2923-2930. |
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Newman DK, Beveridge TJ, Morel FMM. Precipitation of arsenic trisulfide by Desulfotomaculum auripigmentum. Applied and Environmental Microbiology 1997;63(5):2022-2028. |
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Newman DK, Kennedy EK, Coates JD, Ahmann D, Ellis DJ, Lovley DR, Morel FMM. Dissimilatory arsenate and sulfate reduction in Desulfotomaculum auripigmentum sp. nov. Archives of Microbiology 1997;168(5):380-388. |
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Newman DK, Ahmann D, Morel FMM. A brief review of microbial arsenate respiration. Geomicrobiology Journal 1998;15(4):255-268. |
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Supplemental Keywords:
arsenic, anoxic, water., RFA, Scientific Discipline, Water, Environmental Chemistry, Arsenic, Chemistry, Biology, carcinogenesis, arsenic transformation, electron acceptor, microorganisms, anoxic waters, freshwater systems, arsenic exposureProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.